Automatic bidirectional indicator driver

An indicator driver circuit for automatically replacing failed indicator devices, comprising:

• a driving buffer coupled to a current supply as a supply input and a polarity signal input, and transmitting said polarity signal to a first terminal of two indicator devices coupled in parallel;
• current sensing circuitry coupled to said current supply to said driving buffer, operable for detecting when said driving buffer is supplying current to said indicator devices, said current sensing circuitry transmitting a toggle signal which indicates when no current is being supplied to either of said two indicator devices;
• a polarity register coupled to said toggle signal from said current sensing circuitry and transmitting said polarity signal, said polity register changing state responsive to said toggle signal;
• and
• a tristate buffer coupled to a data input signal and to said polarity signal, operable to transmit an inverted version of said polarity signal to a second terminal of said two indicator devices responsive to said data input signal;
• said indicator devices being oriented in opposite directions, so that when said data input signal enables the tristate buffer one of said indicator devices will be forward biased and emit light, and if that indicator device fails to conduct current the current sensing circuitry will transmit said toggle signal to said polarity register and cause said polarity signal to change state, the other one of said indicator devices then becoming forward biased and emitting light.

A method of driving indicator devices irrespective of their orientation, comprising the steps of:

• providing a driving buffer coupled to a polarity signal and having a current supply input;
• providing a plurality of indicator devices having two terminals, a first terminal of each of said indicator devices being coupled to said buffer;
• providing current sensing circuitry coupled to a voltage supply and to said driving buffer, operable for sensing when said driving buffer is driving current to said indicator devices, and outputting a toggle signal when no current is being driven;
• providing a polarity register having an input coupled to said toggle signal, and outputting said polarity signal, operable to invert said polarity signal in response to said toggle signal;
• providing a plurality of tristate buffers coupled to a plurality of inputs, each being exclusively enabled responsive to a respective data input to transmit an inverted version of said polarity signal to a second terminal of a respective indicator device;
• and
• operating said driving buffer, said tristate buffers, said current sensing circuitry and said polarity register such that said polarity register changes state in response to said toggle signal until one of said indicator devices is drawing current responsive to a respective data input, said indicator device thus emitting light irrespective of its orientation.

A method for automatically replacing failed indicator devices, comprising:

• providing a driving buffer coupled to a current supply as a supply input and having a polarity signal input, said driving buffer transmitting said polarity signal to a first terminal of first and second indicator devices coupled in parallel;
• providing current sensing circuitry coupled to said driving buffer, operable for detecting when said driving buffer is supplying current to said indicator devices, said current sensing circuitry transmitting a toggle signal indicating when no current is being supplied to either of said first and second indicator devices;
• providing a polarity register coupled to said toggle signal from said current sensing circuitry and transmitting said polarity signal, said polarity register changing state responsive to said toggle signal;
• providing a tristate buffer coupled to a data input signal and to said polarity signal, operable to transmit an inverted version of said polarity signal to a second terminal of each of said first and second indicator devices responsive to said data input signal;
• and
• placing said indicator devices such that they are oriented in opposite directions, so that when said data input signal enables the tristate buffer a selected one of said indicator devices will be forward biased and emit light, and if that selected indicator device fails to conduct current the current sensing circuitry will transmit said toggle signal to said polarity register and cause said polarity signal to change state, the other one of said indicator devices then becoming forward biased and emitting light.

A bidirectional indicator driver circuit, comprising:

• a driving buffer coupled to a polarity signal and having a current supply input;
• an indicator device including a diode having anode and cathode terminals, one of said anode and cathode terminals being coupled to said driving buffer;
• current sensing circuitry coupled to a voltage supply and to said driving buffer, operable for sensing when said driving buffer is driving current to said indicator device, and outputting a toggle signal when no current is being driven;
• a polarity register having an input coupled to said toggle signal, and outputting said polarity signal, operable to invert said polarity signal in response to said toggle signal;
• and
• a tristate buffer coupled to an input, said buffer being exclusively enabled responsive to a data input to transmit an inverted version of said polarity signal to the other of said anode and cathode terminals of said indicator device;
• said bidirectional indicator driver circuit operable to drive said indicator device independent of which of said anode and cathode terminals is said one terminal and which is said other terminal, said polarity register changing state in response to said toggle signal until said indicator device is drawing current.

A method of driving an indicator device independent of its orientation, comprising the steps of:

• providing a driving buffer coupled to a polarity signal and having a current supply input;
• providing an indicator device including a diode having anode and cathode terminals, one of said anode and cathode terminals being coupled to said driving buffer;
• providing current sensing circuitry coupled to a voltage supply and to said driving buffer, operable for sensing when said driving buffer is driving current to said indicator device, and outputting a toggle signal when no current is being driven;
• providing a polarity register having an input coupled to said toggle signal, and outputting said polarity signal, operable to invert said polarity signal in response to said toggle signal;
• providing a tristate buffer coupled to an input, said buffer being exclusively enabled responsive to a data input to transmit an inverted version of said polarity signal to the other of said anode and cathode terminals of said indicator device;
• and
• operating said driving buffer, said tristate buffer, said current sensing circuitry and said polarity register such that said polarity register changes state in response to said toggle signal until said indicator device is drawing current, to drive said indicator device independent of which of said anode and cathode terminals is said one terminal and which is said other terminal.